The present invention concerns nonwoven materials mainly for personal care products like diapers, training pants, swim wear, absorbent underpants, adult incontinence products and feminine hygiene products. This material may also be used other applications such as, for example, in bandages and wound dressings, nursing pads and veterinary applications.
Personal care articles usually have multiple layers of material of some sort to absorb liquids from the body. These layers may include natural fibers, synthetic fibers and superabsorbent particles in varying proportions. When liquid such as urine is deposited into a personal care product like a diaper, it goes through the uppermost layers, typically a liner against the body and a “surge” layer designed to provide temporary liquid hold-up. The product may also have a “distribution” layer designed to move liquid in the X and Y directions in order to utilize more of the absorbent core. After going through these upper layers, the urine enters the absorbent core portion of the product. The absorbent core permanently retains the liquid. Absorbent cores are typically composed of superabsorbent particles or mixtures of superabsorbent particles and pulp.
Controlling the location of deposition of liquid to the absorbent core and also the rate of absorption of liquid by the absorbent core are very important to the efficient usage of the core. If superabsorbent is allowed to swell uncontrollably, it will eventually block entry of fluid without entirely using the capacity of the superabsorbent located farther into the structure. It is desirable, therefore, to allow superabsorbent to swell in a controlled manner and to a controlled degree so that absorbent core pore integrity is maintained.
Absorbency of superabsorbents may be limited by physical constraints imposed upon the system. The rate of progress of the liquid in the Z-direction, i.e. from point of initial deposition through the product away and from the wearer, may be affected by the permeability of the layers through which the liquid travels. Permeability is in turn affected by such factors as the porosity, wettability and density of the material. Controlling the movement of liquid in the Z-direction also affects the spreading of liquid in the X and Y directions.
Previous methods of controlling the flow of liquid through a product have included the provision of a film layer, which may be apertured, between the liner and absorbent core. This involves additional manufacturing steps in the placing of the film and is relatively expensive. There remains a need, therefore, for a system that will have good liquid intake properties and utilize more of the absorbent core, yet be relatively simple from a manufacturing perspective.